JPS5928472B2 - Method and device for stopping ink jet coating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to dinit drop recording devices, and more particularly to the problem of termination of the printhead within the device upon completion of a desired amount of printing.

These dinit drop recorders use a liquid coating material, such as ink, which is delivered under pressure by a pump to a manifold that communicates with a series of small diameter orifices.

This is suggested in Beam US Pat. No. 3,577,198 and Matis US Pat. No. 3,701,998. When the coating material is expelled under pressure through the orifice, it forms a fine filament of coating material that breaks up into a series of discrete drops. At the point where drops are formed from the filament, they pass a charged electrode that absorbs the coating material depending on the pattern of coating material desired to be recorded on the receiving member that is transported under the drop generator. Each droplet is charged or uncharged. A deflection electrostatic field is set downstream of the charging ring, and all drops that receive a charge while passing through the charging ring are deflected from their trajectory by the deflection field.

A trap is also provided in the ink dinit recording device to capture those drips which it is desirable to prevent from reaching the receiving member. Thus, by applying an appropriate charge signal to the drop, a clear and readable record can be created on the recording medium. The problem of splashing coating materials onto equipment components is
This is critical in ink recording devices because the drip streams need to be closely spaced.

This also requires close orifices and close charged electrodes. With such closely spaced drip streams, it is difficult to keep closely spaced equipment components ink-free, and this ink is electrically conductive and prone to shorts and other electrical cause problems. In addition, the evaporation of the ink leaves scum on the components of the device that accumulates and adversely affects operation. These problems are difficult to resolve during startup and shutdown of the dinit infusion recorder.

For example, if during startup the flow of ink to the drip generator is initiated simply by opening the supply line to the manifold, it will take some time to reach normal operating pressure. During this time, ink initially spills from each orifice, creating a droplet of ink along the bottom of the orifice plate. As the pressure within the manifold increases, the uncontrolled ink dinit is finally ejected from the orifice and stabilizes after the excess ink along the underside of the orifice plate is carried away by the dinit. At rest, the opposite problem occurs.

If the ink supply to the manifold is simply turned off, the pressure will slowly drop and the outflowing ink will languish and
And it ends with ink dripping from the orifice. Obviously, the resulting ink splatters can cause electrical shorts, breaks, and build-up of debris on components. In the past, various attempts have been made to solve this pause problem. for example,
No. 3 to Culp, which suggests the use of a charged electrode with open sides that is moved out of the path of the infusion during startup and rest.
, 618,858, and StOnebu which suggests simultaneously closing the liquid supply inlet valve to the ink manifold and opening the outlet valve from the manifold to the vacuum source.
No. 3,891,121 and Per.
No. 4,042,937 to Ry et al. However, none of these conventional suspension methods were completely satisfactory.

The use of movable charging electrodes makes the recording device more complex, and the closing of the liquid supply and the simultaneous opening of the vacuum source and ink supply manifold creates pressure oscillations within the manifold, and the ink supply Allowing air and other contaminants to be drawn into the equipment. This requires an additional cleaning step to remove air and contaminants afterwards.
The problem of achieving clean shutdown is particularly acute in office copiers where ink is maintained in the manifold at all times to enable prompt start-up of the digital recorder.

The cleaning step required before each start-up significantly lengthens the start-up time for each copying cycle, which is highly undesirable. Therefore, there is a need for a simple shutdown process to prevent ink splashing and to keep air and other contaminants out of the ink supply system. An ink generator provided in accordance with the present invention includes an ink generator head housing an ink manifold and a multijet orifice plate.

A pressurized ink supply is connected to the manifold via an inlet valve. At the outlet end of the manifold, a second valve connects the manifold to a vacuum source. A controller is also provided to properly sequence the opening and closing of the valves. During operation of the ink dinit recording device, the inlet valve to the manifold is open, but the outlet valve is closed.

At rest, the inlet valve to the manifold closes and the pressure within the manifold begins to drop. This pressure drop is monitored by the controller until it reaches a point just above the minimum operating pressure required to maintain proper dinit drip flow linearity.
do. When that point is reached, the outlet valve opens and the vacuum source quickly terminates the flow of ink through the orifice to provide a clean pause. It is therefore an object of the present invention to provide a simple and reliable method and apparatus for ensuring clean shutdown of an ink dinit recording device.

A clean pause is the cessation of ink flow in a dinit recording device without dripping or splashing of ink from the orifice and without ingesting air or other contaminants from the orifice; and to keep the GINIT recording device ready for restart without the need for cleaning or purging. The present invention will be described below with reference to the drawings.

As shown in FIG. 1, a liquid coating material, such as ink, is supplied from a container 10 by a pump 11 through a conduit 12 and an inlet valve 14 to a recording head 16.

Recording head 16, shown schematically for ease of understanding, is preferably of a laminated construction as generally suggested in BO U.S. Pat. No. 3,586,907, and includes longitudinally spaced dinit rows. Occur. If desired, the recording head can be
Dinit rows arranged in two parallel rows may be generated as suggested in U.S. Pat. No. 3,701,998 to Athis. Typically, orifices 18 within recording head 16 are approximately 0.02 mm to 0.05 U1 in diameter and spaced approximately 0.5 mm1L apart on centers. The major components of recording head 16 are liquid coating supply manifold 20, orifice plate 22, charge ring plate 24, deflection electrode 26, and capture device 28.

Ink within manifold 20 flows out through orifice 18 under pressure created by pump 11 to form drip stream train 30 . The non-biased drops are printed in a readable pattern on the web 32. Positive pressure within manifold 20 is required for ink flow through orifice 18. Outlet valve 34 connects the outlet of manifold 20 to vacuum source 36
Connect to. Outlet valve 34 and inlet valve 14 are preferably solenoid valves operated by electrical signals from controller 38. In a preferred embodiment, pressure sensing transducer 40
is also connected to the manifold 20 to detect any pressure changes within the manifold. Additionally, transducer 40 is electrically connected to controller 38 . During normal operation of the recording device,
The coating material such as ink is approximately 30p below atmospheric pressure.
si high pressure (all pressure references are atmospheric pressure) to the manifold.

This normal operating pressure will vary somewhat depending on the viscosity of the particular coating material used and the diameter and shape of the orifices within the orifice plate. However, for typical water-based dinit printing inks having viscosities of 1 to 3 centiboads and orifices having diameters of 0.85 to 2.0 mils, operating pressures of 12 to 30 psi provide satisfactory dinit flow straightness. do. To initiate shutdown of the recording device, controller 38 sends an electrical signal to cause inlet valve 14 to close.

A straight stream of ink drops continues to eject from the orifices as the pressure within manifold 20 drops. As shown in Figure 2a, when the inlet valve closes, the pressure in the supply manifold is
It descends for a few seconds until it reaches essentially atmospheric pressure. However, at some point during the pause, the pressure within the manifold drops below the minimum pressure necessary to maintain dinit flow linearity. For typical water-based dinit printing inks, this minimum pressure is about 8 to 10 psi. If no further action is taken, the pressure in the manifold will drop below its minimum pressure and the dinit flow will go out of control, splashing ink onto the components of the recording device. However, this ink splashing problem is resolved at or slightly above the minimum operating pressure, and the controller opens the outlet valve 34 to the vacuum source 36. As shown in Figure 2b, opening the manifold to a vacuum source essentially instantly causes the pressure within the manifold to drop to atmospheric pressure. Due to the surface tension of the coating material and the small size of the orifice, the interflow exiting the orifice immediately terminates and leaves it at rest cleanly. It has been found that only a small vacuum needs to be drawn to achieve this result.

Typical water-based dinit printing inks produce good results at vacuums as low as 0.2 to 0.8 psi below atmospheric pressure. If a higher vacuum is drawn, air and other contaminants will tend to be drawn into the manifold, whereas if a lower vacuum level is drawn, some coating material will leach out of the orifices. Naturally, the viscosity of the coating material used and the dimensions of the orifice will influence the optimum vacuum value required. The control system consists of a simple timing mechanism which operates to open the outlet valve 34 a predetermined time after the inlet valve 14 is closed.

This timing can be adjusted depending on the particular coating material used. The time required to reduce to the minimum pressure to maintain linearity of the dinit varies depending on the characteristics of the coating material, valves, and manifold volume. A smaller ink manifold reduces the usage time of plunger type solenoid valves. Thus, the total time varies from 2.5 seconds as shown in Figure 2b to a value as small as 0.05 seconds. However, in the preferred embodiment, the pressure sensing transducer 40 senses the pressure within the manifold 20 and energizes the controller 38 such that the controller detects the minimum pressure required to maintain dinit flow linearity. When the pressure in the manifold is at or slightly above the limit pressure, the outlet valve 34 is opened. Similarly, the controller can be adjusted for the particular coating material and orifice used within the recording device. As described in detail above, in accordance with the present invention, the ink flow is controlled by opening the outlet valve 34 to a vacuum source after the pressure within the manifold 20 has been reduced to a minimum operating pressure or slightly higher. It reduces the pressure drop required to shut down the manifold and allows the use of very little vacuum without drawing air or other contaminants into the manifold.

Further in accordance with the present invention, the inlet valve is closed during periods of inactivity to prevent ink from entering the manifold, and the application of the vacuum source is delayed until the minimum operating pressure is reduced to reduce the instantaneous pressure drop. This makes it possible to prevent vibrations in the ink pressure within the manifold. This is a conventional device,
That is, it is advantageous over devices in which the ink flow is interrupted and at the same time the ink is exposed to a source of negative pressure. In such prior art devices, a relatively high vacuum source had to be used because the pressure within the ink supply manifold had to be reduced instantaneously from a relatively high pressure to a low pressure.
This high vacuum source not only reduced the pressure within the ink supply manifold, but also caused air or other contaminants to be drawn into the print head. When such air or the like is inhaled, the contaminants must be removed by purging or cleaning prior to starting the device. Therefore, the present invention is highly effective in overcoming the above-mentioned drawbacks of conventional devices and achieving clean shutdown of dinit recording devices. Although the apparatus and method described above constitute preferred embodiments of the invention, the invention is not limited to the detailed method and apparatus, and modifications may be made without departing from the scope of the invention. .

[Brief explanation of the drawing]

FIG. 1 shows a typical dinit drip coating device with a control system and inlet and outlet valves. Figures 2a and 2b are graphs of pressure drop versus time within the manifold of a dinit drip coating device. Explanation of symbols, 10: liquid]-teing substance supply device, 11: pump, 12: conduit, 14: inlet valve,
16: recording head, 18: orifice, 20: manifold, 22: orifice plate, 24: charging ring plate, 26:
Deflection electrode, 28: Capture device, 30: Drip stream train, 32: Web, 34: Outlet valve, 36: Vacuum source, 38: Control device, 4
0: Pressure detection transducer.

Claims (1)

Claims: 1. A pressurized coating material comprising a plurality of orifices, a manifold for delivering liquid coating material to the orifices, an inlet valve, and an outlet valve connected to a vacuum source. Coating connected to supply device
A method of shutting down an ink jet coating apparatus having a head, the method comprising the steps of: b) closing the inlet valve; and b) instantaneously reducing the pressure in the manifold to ambient air pressure at a point where the pressure in the manifold is slightly higher than the minimum pressure required to maintain normal operation. opening the outlet valve to the vacuum source in close proximity and at a strength that does not make the pressure within the manifold more negative than ambient air pressure; 2. The method of claim 1, including the step of detecting a pressure drop within the manifold. 3 The vacuum source is 0.2 to 0.8 below the ambient air pressure.
3. The method of claim 2, wherein the psi is low. 4 The minimum pressure required to maintain normal operation is 8
4. The method of claim 3, wherein the psi. 5. The method of claim 4, wherein the outlet valve opens from about 0.05 seconds to 2.5 seconds after the inlet valve closes, depending on device characteristics. 6. A jet drip coating apparatus comprising a coating head provided with a plurality of orifices and a manifold for applying liquid coating material to said orifices, comprising: a) an inlet of said coating head; b) an inlet valve connected to said inlet; c) an outlet of said coating head; d) an outlet valve arrangement connected to said outlet; e) a vacuum source connected to said outlet valve arrangement; and f) said inlet valve arrangement, said outlet valve arrangement and said electrically connected to a manifold, closing the inlet valve arrangement and instantaneously reducing the pressure in the manifold at a point where the pressure in the manifold is slightly above the minimum pressure required to maintain jet straightness. and a control device for opening the outlet valve arrangement to the vacuum source of a strength that approximates ambient air pressure but does not make the pressure in the manifold more negative than ambient air pressure. 7. The pause device of claim 6, wherein the control device includes a pressure sensing transducer for detecting a pressure drop within the manifold. 8. The deactivation device of claim 6, wherein said control device includes a preset timing device actuated by closure of said inlet valve device to determine when said outlet valve device is to be opened. 9. A pause device according to claim 7 or 8, wherein the vacuum source is 0.2 to 0.8 psi lower than the pressure of the surrounding air. 10. The shutdown device according to claim 6, wherein the inlet valve and the outlet valve are solenoid valves.